In a cutterhead of this type, known from U.S. Pat. No. 4,104,796, opposed coupling members configured as sliders are provided in a rotatably mounted casing and are each biased by a helical spring; at a predetermined centrifugal force, the sliders slide outwardly counter to the force of the springs. This releases the coupling connection between the sliders and the cams on the spool so that the spool can rotate to feed out the cutting filament to some extent. After the centrifugal force drops because of the readjustment of the cutting filament, the helical springs force the sliders back into their initial position, so that one of the cams abuts the slider thereby fixing the spool. The cutting filament can be fed out again only after the predetermined centrifugal force is reached in response to the cutting filament becoming shorter due to wear whereupon the sliders slide outwardly to again unlatch the spool.
A substantial disadvantage is that the sliders, guided linearly, come into action independently of one another in order to release the spool in dependence upon centrifugal force. If in fact one of the two sliders does not shift synchronously with the other slider, for instance because it has become soiled and the friction on the two sliders differs, then either the detent coupling does not index at all, or the spool is permanently released thereby allowing the cutting filament to unreel freely. The known cutterhead is therefore quite vulnerable to malfunctioning as a function of the varying friction of the two sliders in their guideways. This cutterhead is also expensive to manufacture because the parts must be very accurately configured and guided.
In another cutterhead, of a different type, a single pivotable lever is provided on the housing. This lever is somewhat similar to the swinging of a spring clockwork and has two stops, which cooperate in alternation with cams of the spool that rest tightly beside one another like toothed rings.
In still another cutterhead, disclosed in European patent application No. 84307043.4, the release of the camlocked spool is effected as a function of centrifugal force by the rise or upward travel of balls shifting on inclined surfaces; as a result, lower stops located on the spool become disengaged from the associated counterstops, and the upper stops release the length of the cutting filament by rotating the spool a predetermined amount. After readjustment, that is, after the cutting filament has been lengthened, the force of the spring located in the housing lid predominates and forces the rotatable spool back into its initial position, because the lessening of centrifugal force causes the balls to return to their initial position. The disadvantage here is that during the cutting operation, the cutting filament does not always assume an exactly horizontal position; instead, it may extend obliquely either upwardly or downwardly, depending on the resistances encountered during cutting. As a result, there are centrifugal force components of various magnitudes in the vertical direction which can have an uncontrollable effect on readjustment. It may even happen that when the balls begin to move upwardly, a premature and unintentional resonance buildup due to unpredictable vertical centrifugal force components may bring about the triggering or lowering operation, resulting in a continuous adjustment regardless of the rotational speed.